This scene can be roughly divided into three: the Witches' casting of a spell; the supernatural answers to Macbeth's demands; and Macbeth's return to the cold world of political and social reality. The scene's structure deliberately recalls the opening scenes of the play. Once more, Macbeth's destiny is in question. Once more, he receives three prophecies. Once more, he is left on his own to decide how best to interpret those prophecies. And once more he fails to understand that Fate is inevitable, however he chooses to act.
The Witches' charm is fantastic: Its ingredients, thrown into a bubbling cauldron, are all poisonous. Moreover, these ingredients are all the entrails or body parts of loathed animals or human beings, which, taken together, can be interpreted as making a complete monster: tongue, leg, liver, lips, scales, teeth, and so on. The strong implication is that Macbeth himself is no longer a complete human being; he himself has become a half-man, half-monster, a kind of chimera.
Macbeth arrives at the Witches' lair with extraordinary boldness, knocking at the entrance in a way that ironically recalls the entry of Macduff into Macbeth's castle in Act II, Scene 3. When he "conjures" the Witches to answer him, his language is uncompromising: He matches their power with a powerful curse of his own, demanding to have an answer even if it requires the unleashing of all the elements of air, water, and earth; even if all the universe — natural or manmade — "tumble" into ruin. His most defiant act, by far, is to desire to hear the prophecy of his future not from the Witches, who are themselves only "mediums" of the supernatural, but from their "masters," that is, the controlling Fates.
